This invention relates to an improved radial face seal and, more specifically, to a self-stabilizing radial face seal.
Face-type fluid seals are shaft seals generally comprising a nonrotating or stationary seal face and a rotor ring provided to rotate with the shaft and having a face opposing that of the stator seal, the opposing faces extending radially outwardly from the periphery of the shaft, thereby effecting a seal between the low-pressure and high-pressure regions of a surrounding and engulfing fluid. Radial face seals operate with extremely small gaps between the stationary or primary seal ring and the opposing face of the rotor ring or seal seat. It is necessary that the tolerances for the existing space or gap be closely monitored so that the existing gap is held as closely as possible to its design value so as to avoid excessive fluid leakage or high friction loss. To realize this, the primary seal ring must be placed in a stabilized condition both under hydrostatic as well as hydrodynamic conditions. That is, proper equilibrium must be reached between high-pressure and low-pressure regions both under conditions when the liquids involved are at rest and to the pressures they exert or transmit as well as under conditions when motion of the fluids exert a force which acts on the elements of the seal immersed in the fluids.
Conventional radial face seals consisting of a primary seal ring or stator member and a rotor seal ring are inherently unstable, generally due to an angular misalignment brought about by hydrodynamic effects establishing a pressure differential which produces a transverse moment which alters and disturbs the seal of the primary or stator seal ring. This pressure distribution produces the dynamic instability having a detrimental effect upon the resulting seal.
It has been found that means must be provided within a face-type fluid seal so as to eliminate the instability created with respect to the seal as a result of the hydrodynamic effects within the system. One approach in the design of the face-type fluid seals to control the seal performance and to accommodate the axial movement has been to isolate both the rotor and the stator from the pump housing. A discussion of such a design for hydrostatic seals may be found in ASME Publication 68-WA/LUB-9, "The Spring-Supported Hydrostatic Seal", by I. J. Billington and T. E. Fitzsimmons. However, it is not desirable to be relegated to a system whereby it is necessary to isolate the rotor and stator from the pump housing.
It has further been found that it is important that the stator ring of the face-type fluid seal be well supported relative to the housing and adapted so as to resist annular overturning moments which may act on the stator ring. To achieve this purpose, a stator ring has been proposed having a support annulus formed on the back face thereof through which there may be a force transmitted which tends to oppose any overturning moment which develops on the ring. Although achieving certain desired results, this approach is not without its disadvantages. For example, the annulus is fixed or becomes a part of the stator ring and subject to imperfections as well as wear which reduces the dependability of the proposed system. Furthermore, slots must be cut in the support annulus so as to provide for pressure communication of the fluid in the system. The purpose of the support annulus is to provide an additional force acting against the back face of the stator seal so that the additional force tends to overcome the overturning moments created by the hydrodynamic system. However, with the use of an annulus of the nature herein described, the incumbent system becomes inflexible in that the position of the support annulus is quite critical and not adaptable to a change in the force vectors necessary to oppose the overturning moment produced within the system. Thus, the manufacturing tolerances of such a member are such that the support annulus cannot always be machined to assure that it will contact the support face throughout its entire length. Thus, the material requirements in fabricating the support annulus become critical.